Design And Research Of Microfluidic Reactor With High-frequency Vibration And Self-circulation Based On Piezoelectric Drive

Microfluidic reactors have a great advantage in the chemical field because of their low consumption of reagents,high reaction efficiency,safety,controllability and so on.At present,most researches of microfluidic reactors focus on the rapid mixing and precise proportion and few researches are launched on the reaction requiring some space and time.In this paper,based on the piezoelectric driving technology and the fabrication process of piezoelectric micro pump,a kind of microfluidic reactor with high-frequency vibration and self-circulation is proposed.On the one hand,it utilizes the active self-circulation of the piezoelectric micro pump to promote uniform mixing of the solution.On the other hand,it uses the high-frequency vibration of the vibration substrate to balance reaction conditions and inhibit the agglomeration between particles.So it is a more active,process controllable new microfluidic reactor.It is suitable for complex reactions,long time reactions,chemical reactions requiring active mixing,and especially for the liquid-phase synthesis reaction of noble metal nanoparticles.The overall research contents are as follows.The theoretical bending model of piezoelectric vibrator was established to obtain the parameters of the maximum deflection of piezoelectric vibrator.The modal analysis and harmonic analysis of piezoelectric vibrator were carried out by ANSYS software.It was found that the first order vibration mode was a pure bending mode,and when the excitation frequency was the resonant frequency of the piezoelectric vibrator,it would respond with the largest displacement and the most driving ability.The fluid simulation analysis models of the mixing pool were established by COMSOL software.The flow characteristics showed that when the inlet Reynolds number was high,the vortex flow would be formed in the mixing tank and the mixing could be dominated by convection.The more obvious the vortex was,the better the mixing would be.The simulation results also showed that the U-shaped structure was the optimal structure of the single inlet and outlet distribution.It also showed that W/D=1/12 was the best structural parameter.Based on the characteristics of the U-shaped structure,the structure of the mixed pool with multi inlet and outlet distribution was better than that of the single inlet and outlet distribution.Adding Round-shape obstacle or Leaf-shaped obstacle to the middle of the mixing tank did not have a significant impact on enhancing mixing.The piezoelectric driven microfluidic reactor was designed and manufactured,and the performance tests on piezoelectric micro pump,self-circulating reflux and vibration substrate were carried out.The test results showed that the output flow and output pressure of the piezoelectric micro pump increased linearly with the increase of the driving voltage.When the driving frequency was at 80~120Hz,piezoelectric micro pump output flow rate and pressure were all at a high level.And when the driving frequency at 160~200Hz,the output flow of piezoelectric micro pump was small,but the fluctuation of frequency on the impact of flow rate was little.Under the condition of the driving frequency of circulating pumps at 100 Hz,the vortex speed became faster with the increase of the driving voltage.When the voltage was at 80 V,the vortex speed rearched up to 263r/min.In the case of the mixing tank filled with 0.4 ml of water,the resonant frequency of the vibrating substrate was 3.85 kHz,and at this frequency,the maximum amplitude increased as the voltage increased.When the voltage was at 100 V,high-frequency vibration could disperse magnetic ceramic particles,and when the voltage was greater than 120 V,it would produce atomization.The microfluidic reactor made in lab was used to research the controllable liquid-phase synthesis of silver nanoparticles,which verified its advantages in application of complex chemical reactions.Experiment results showed that as a protective dispersant,PVP could effectively inhibit the agglomeration of silver nanoparticles.Self-circulation reflow had an effect on the synthesis of particle particles.With the increase of the driving voltage,the vortex flow became faster and the reaction became more uniform,which was conducive to the synthesis of silver nanoparticles with better sphericity and higher dispersity.High-frequency vibration could also affect the synthesis of particles.Only when the driving frequency was the resonant frequency,the vibration substrate could play the best effect of high frequency vibration,which could not only balance the growth environment of particles,but also inhibit the agglomeration of nanoparticles.The effect of concentration ratio of Silver Nitrate and Sodium Nitride on nanoparticles was also analyzed experimentally.When the concentration ratio was 1: 4,the synthesized silver nanoparticles had the highest concentration,the smallest size distribution,the highest sphericity,and the best dispersibility,as well as the average size of which was 9.86 nm.